Buildings with pitched roofs usually have open and unheated attics. Insulation for the room below is usually provided by fibrous insulation above the horizontal ceiling. If the insulation blocks airflow from the soffit vents at the eaves to attic vents, usually at the pitch peak, heat loss at the eaves may occur and with freezing and thawing temperatures, ice dams may form at the eaves causing roof leaks usually in the coldest of weather. In the summer, improper ventilation of the attic can lead to significant thermal inefficiency, excess humidity and other problems. It is accordingly desirable that proper ventilation from the lower eaves to the attic vents be maintained to avoid such heat and moisture problems.
To achieve such venting, a wide variety of sheet-like products have been used which are fastened to the underside of the roof between the rafters. Such products may include flanges providing ease of fastening and a spaced or offset wall forming open troughs extending end-to-end. It has been found that such products made from extruded foam polystyrene sheet have excellent break resistance and resist moisture so they will not rot or deteriorate. Extruded polystyrene has greater strength than simply expanded polystyrene such as bead board or sheet.
The lateral space of the trough or airway, however, creates a flexure problem, particularly at the ends of the sheet. It has, accordingly, been found advantageous to provide a stiffening ridge along the center of the trough end-to-end. However, when forming large extruded foamed polystyrene sheet between precision matched metal dies, the forming process attenuates the sheet reducing the wall thickness of the sides of the ridge. This in turn lessens the compressive strength of the ridge. Also, particularly along the root of the base and at the apex of the ridge, the corners are in effect creases, and with the reduced wall thickness of the ridge, such corners become a possible point of failure, particularly in handling and installation.
Accordingly, it would be useful to have a trough ridge from end-to-end of the panel where the corners or creases of the ridge were strengthened and without significantly obstructing the airway through the trough on each side of the ridge.